1. Field
The present invention relates to a pulse wave measuring device for measuring a pulse wave while being put on a human body.
2. Description of the Related Art
One of devices that measure vital-sign information about a user while being put on a body, such as a wrist, is a pulse wave measuring device that optically measures a pulse wave.
A pulse wave is a waveform arising when a change in the pressure of blood stemming from contraction of the heart travels to peripheral blood vessels, and the waveform is primarily induced by a change in the flow of arterial blood. However, amounts of hemoglobin in blood acquired at an area to be measured also change in the same manner as does the flow of arterial blood, and hence a pulse wave can be measured by means of measuring the amounts of hemoglobin.
One technique for measuring a pulse wave is a photoelectric pulse wave detection method. A light absorption factor of hemoglobin changes depending on the wavelength of light. Light in a waveband (ranging from visible light to near infrared light), which is absorbed by hemoglobin, is radiated from a light-emitting element (LED: a light-emitting diode, and the like). Differences in the intensity of reflected light or transmitted light induced by a change in blood flow are detected by a light-receiving element (a photodiode, and the like), thereby detecting a pulse wave.
Depending on a waveband to be used, a change in blood flow of an arteriole near skin is captured by means of pulse wave detection complying with the photoelectric pulse wave detection method; hence, pulse wave measurement is suitable for measurement performed in an area (a finger, a palm, an ear lobe, and the like) where a plurality of arterioles are present. (For example, refer to JP-A-2003-169780 (KOKAI)).
A device for measuring a pulse wave without placing a burden on the user in a daily life has already been put into commercial production. For instance, a main unit of a pulse wave measuring device is put on a wrist like a wrist watch, and only a pulse wave sensor is withdrawn from the main unit by means of a cable. The pulse wave sensor is wrapped around a finger, to thus measure a pulse wave in a palm. However, wrapping the pulse wave sensor around a finger hinders daily living activities, such as washing hands and gripping an object. For this reason, it is desirable to measure a pulse wave at a wrist where the main unit of the pulse wave measuring device is put. However, signal intensity acquired through photoelectric pulse wave measurement performed at a wrist is weaker than that acquired through measurement performed in a palm, and there is the case where measurement cannot be performed stably depending on the user or a state.
In a pulse wave measurement device that enables selective use of a removable pulse wave sensor for finger use and a wrist pulse wave sensor for measuring a pulse wave at a wrist, it is laborious for the user to specify and switch the pulse wave sensor to be used for measurement.
Therefore, it is appropriate that the pulse wave measuring device should determine connection/disconnection of the finger pulse wave sensor and automatically switch operation of the pulse wave measuring device so as to measure a pulse wave at a finger when the finger pulse wave sensor is connected and at a wrist when the finger pulse wave sensor is not connected.
It is conceivable that an electrical connection detection mechanism will be provided in a connector for detecting connection of the finger pulse wave sensor. Proposed as such is a mechanism having a logical output circuit using; for instance, a GND pin provided in a cable terminal, thereby detecting connection/disconnection of an external input device (see; for instance, JP-A-2006-33127(KOKAI)). Provision of a mechanical connection detection mechanism is also conceivable. For instance, a connector equipped with a contact switch for detecting connection is proposed (see; for instance, JP-A-2006-80816(KOKAI)).
However, miniaturizing the connector of the pulse wave measuring device of wrist watch type as small as possible is desirable.
When the detection technique, such as that described in connection with JP-A-2006-33127(KOKAI), is adopted, provision of an electrode for detecting connection is required, which results in an increase in the number of electrodes as well as the number of signal lines and an increase in the size of the connector.
When the detection technique, such as that described in connection with JP-A-2006-80816(KOKAI), is adopted, a mechanical mechanism is provided; hence, there is a disadvantage of requirement of a space for the mechanism and complication of the mechanism itself.